1. Field of the Invention
The present invention relates to a mask for evaporation, a mask frame assembly including the mask for evaporation, and methods of manufacturing the mask and the mask frame assembly, and more particularly, to a stack structure of a material which forms a mask for evaporation, and an improved method of manufacturing the mask using an electro-deposition method.
2. Description of the Related Art
FIG. 1 shows a conventional mask 10 used to evaporate organic films or electrodes during the manufacture of organic electroluminescent display devices. The mask 10 is supported by a frame 20 so as to apply tension to the mask 10. The mask 10 has a structure in which predetermined slots 11 are formed to form a plurality of organic films or electrodes on a thin film. The mask 10 can be manufactured through an etching method or an electro forming method.
According to a conventional etching method, a photoresist layer having a slot pattern is formed on a thin film by a lithography method, or a film having a slot pattern is attached to a thin film. Thereafter, the thin film is etched. However, with an increase of the size of the mask and an increase of fineness of the slot pattern, the conventional etching method does not match or meet width and edge allowances for the slots 11. In particular, when the mask 10 is manufactured by etching a thin film, where the thin film is over-etched or under-etched, the size of the slots 11 is not uniform.
According to a conventional electro forming method, a metal is evaporated on a matrix to a desirable thickness, due to electrolysis of a metal salt by an operation such as an electroplating, and is then lifted from the matrix, thereby forming an electrocasted product having reverse concaves and convexes to the matrix. The mask 10 is manufactured using the above-described principle. In the electro forming method, the mask 10 is formed of an alloy of nickel (Ni) and cobalt (Co). When this alloy is used, high surface roughness and high precision of a slot pattern can be achieved. However, cracks occur in the mask 10 during a welding of the mask 10 to the frame 20 due to the bad welding characteristic of the alloy. In other words, where cobalt is alloyed with another metal, both hardness and stiffness increase, thereby increasing the fragility. Accordingly, as shown in FIG. 2, cracks easily occur during a welding of the mask 10 to the frame 20, where the mask 10 is manufactured using the conventional electro forming method.
Embodiments of a conventional mask frame assembly are disclosed in Japanese Patent Publication Nos. 2000-60589, 1999-71583, and 2000-12238.